The present invention relates to an intake pipe.
For example, in a gasoline engine, air is drawn through an inlet of an intake pipe is mixed with fuel injected by a fuel injection valve, and the air-fuel mixture is burned in a combustion chamber. In recent years, engines of large displacement are equipped with an intake pipe having a plurality of inlets to supply a greater flow rate of air to combustion chambers. Japanese Laid-Open Patent Publication No. 2004-169688 discloses such an intake pipe that has two passages to draw air to an engine. Each passage has an inlet and an air cleaner.
In this intake pipe, when the flow rate of air (intake pressure) drawn through a first inlet 10a is different from that of a second inlet 10b as shown in FIG. 16, some of the air that has passed through a first passage 50a can flow to a second passage 50b without flowing to a throttle body 40. FIG. 16 illustrates a case where the intensity of air flow produced as a vehicle moves varies from left to right. That is, FIG. 16 shows the flow of air taken through the first and second inlets 10a, 10b. Arrow A shows the flow of air that is taken through the first inlet 10a and flows to the throttle body 40. Arrow B shows flow of air that is taken through the first inlet 10a and flows into the second passage 50b via a confluence portion 55 of the first and second passages 50a, 50b. 
In such a case, some of the air that should be flowing to the throttle body 40 flows into the second passage 50b. This causes supply of air to the combustion chambers to be insufficient. As a result, the intake efficiency of an engine 30 can deteriorate. The air that flows into the second passage 50b disturbs output signals from first and second air flowmeters 70a, 70b, causing errors in measured values of the flow rate of air. Particularly, to comply with the current emission control, the air flow rate is desired to be accurately measured.